This invention relates in general to a "dual mode" drum brake assembly which includes a hydraulically actuated service brake of the leading/trailing type, and a mechanically actuated parking and emergency brake of the duo-servo type.
One version of a dual mode drum brake is disclosed in Australian Patent No. 53,491. In this patent, a hydraulic actuator, used for applying the service brakes, is located adjacent the upper ends of a pair of brake shoes, while a fixed abutment is located adjacent the lower ends. This arrangement provides a service brake of the leading/trailing type. The brake further includes an upper strut which is located adjacent the hydraulic actuator and extends between the brake shoes, and which is provided with an automatic adjusting mechanism. A parking brake actuating lever is pivotally mounted on a lower end of one brake shoe, and an idle lever is pivotally mounted at an intermediate point on the other brake shoe. A lower strut extends between the brake shoes adjacent the lower abutment and is disposed between a lower end of the parking brake lever and a lower end of the idle lever. When pivoted, the parking brake actuating lever extends the effective length of the lower strut and pivots the idle lever to initiate duo-servo actuation of the parking brake
Other versions of dual mode drum brakes are disclosed in U.S. Pat. No. 3,400,787 to Keller et al., U.S. Pat. No. 3,709,334 to Kondo et al., U.S. Pat. No. 4,364,456 to Colpaert, and U.S. Pat. No. 4,678,067 to Thompson.